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Remnant clouds from Blanca are seen in the middle of this GOES-12 satellite image, as it sits in the open waters of the Eastern Pacific Ocean. Credit: NASA/NOAA GOES Project
Blanca Hits a "Remnant" Low

Blanca's run in the Eastern Pacific Ocean has come to a close as the tropical cyclone has "hit a remnant low" pressure status on its way to total dissipation.

At 11 p.m. EDT on July 8, the National Hurricane Center deemed Blanca a remnant low pressure area and issued their last advisory on the cyclone. At that time, its sustained winds were down to 30 mph, and it was weakening in waters too cool to sustain it. Blanca's last minimum central pressure was 1006 millibars. By 9 a.m. EDT on July 9, Blanca's remnants had moved to a position about 830 miles west of the southern tip of the Baja California.

During the early morning hours of July 9, some thunderstorms were still occurring in Blanca, but the system lacked the deep convection (rapidly rising air that forms more thunderstorms and keep the storm going). There may be more thunderstorms that pop up around Blanca's weak circulation over the next day or two until it totally dissipates sometime before July 11.

The Geostationary Operational Environmental Satellite, GOES-12, captured Blanca's remnants at 7:45 a.m. EDT (1145 UTC) on July 9 in the open waters of the Eastern Pacific Ocean. GOES-12 is operated by the National Oceanic and Atmospheric Administration, and the image was created by NASA's GOES Project, located at NASA's Goddard Space Flight Center, Greenbelt, MD.

Although Blanca is fading, the National Hurricane Center is watching another area in the Eastern Pacific about 950 miles south of the southern tip of Baja California. There is an area of disturbed weather there, and it has a low chance of developing into a tropical depression over the next 2 days.

Blanca was a tropical storm on July 7 and by early morning today, July 8, she had weakened into a tropical depression. Now, as she continues to move into cooler waters Blanca is expected to become a remnant low late tonight. NASA's Aqua satellite captured an infrared image that showed that the clouds in the storm are already coming apart and weakening.

At 5 a.m. EDT on July 8, the National Hurricane Center noted that Blanca had weakened to a tropical depression. At that time, Blanca's maximum sustained winds were near 35 mph, but keeps moving further into cooler waters that are sapping its strength. The storm has continued to move away from the west coast of Mexico and was located about 600 miles west-southwest of the southern tip of the Baja California. That put the storm near 20.8 north latitude and 119.0 west longitude. Estimated minimum central pressure was 1004 millibars.

The Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua satellite captured Blanca's clouds coming apart on July 7, 2009 at 4:53 p.m. EDT (20:53 Zulu Time) in an infrared image. The image shows a storm that is no longer circular or even "comma shaped" as it was the day before.

The infrared image is useful to forecasters because it shows the temperature of the clouds. NASA false-colors clouds at different heights in the infrared satellite images, so that the highest clouds appear purple, and the second highest clouds appear in blue. How does infrared imagery know how high clouds are in the sky? The coldest ones are higher in the sky (because in the troposphere, the lowest layer of atmosphere where weather happens, temperatures fall the higher up you go until you get to the stratosphere).

In infrared imagery, NASA's false-colored purple clouds are as cold as or colder than 220 degrees Kelvin or minus 63 degrees Fahrenheit (F). The blue colored clouds are about 240 degrees Kelvin, or minus 27F. The colder the clouds are, the higher they are, and the more powerful the thunderstorms are that make up the cyclone.

Because the infrared imagery reads temperature it can also tell how warm the ocean waters are the surround a storm. Warmer temperatures are also false-colored and an orange color represents temperatures of 80F (300 degrees Kelvin).

By Friday, July 10, forecasters expect that Tropical Depression Blanca will have "blanked out."

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Blanca's cold clouds and thunderstorms are seen in purple in this AIRS satellite image. Credit: NASA JPL, Ed Olsen
Blanca Moving Out to Sea and Into Cooler Waters

Tropical Storm Blanca has made the move away from the western Mexican coast, and is heading out to sea in a west-northwest direction near 9 mph. Blanca's course will take her further out to sea and into cooler waters which will weaken the storm.

As a tropical storm, Blanca is generating a good amount of rainfall over the open ocean. NASA and the Japanese Space Agency's Tropical Rainfall Measuring Mission (TRMM) Satellite acts like a "rain gauge in space" and can estimate rainfall in storms. On July 6 at 12:09 a.m. EDT (0409 UTC) TRMM flew directly above Blanca and captured an image of rainfall happening throughout the storm.

Creating an image of TRMM's rainfall in a storm takes some doing. Hal Pierce at NASA's Goddard Space Flight Center in Greenbelt, Maryland, where TRMM is managed, assembles images from various TRMM instruments.

To create an image of rainfall analysis, Hal uses data from the TRMM Microwave Imager and Precipitation Radar instruments and overlays it on a TRMM infrared image. The analysis shows heavy rainfall of over 50 millimeters per hour (~2 inches) in an area east of the center of circulation.

The AIRS infrared images are false-colored to show Blanca's highest, cold clouds in purple and blue. Those temperatures are as cold as or colder than 220 degrees Kelvin or minus 63 degrees Fahrenheit (F). The blue areas are around 240 degrees Kelvin, or minus 27F. The colder the clouds are, the higher they are, and the more powerful the thunderstorms are that make up the tropical storm.

During the morning hours of July 7, Blanca had sustained winds near 50 mph with higher gusts. Because she's moving into cooler waters, and it takes water temperatures of 80 F to maintain a tropical cyclone, Blanca is expected to weaken over the next two days. At 5 a.m. EDT on July 7, Blanca was about 425 miles southwest of the southern tip of Baja California. That puts the center of the storm near latitude 18.5 north and 114.5 west.

Blanca started out as an area of low pressure southwest of Mexico was upgraded to tropical storm Blanca during the morning of July 6. Blanca is the second named tropical storm in the eastern Pacific this hurricane season and isn't expected to become a hurricane.

> View larger image This combination image of Blanca from the TRMM and GOES-11 satellites show rainfall and cloud cover of the storm on July 6, 2009. Credit: Naval Research Lab/JWTC/NASATropical Storm Blanca and a Two-Satellite Combo

The second tropical storm of the eastern Pacific Ocean hurricane season formed off the western coast of Mexico, and data from two satellites are giving meteorologists a comprehensive look at its clouds and rainfall.

The TRMM image was captured on July 6 at 0410 Zulu Time (12:10 a.m. EDT), and it was combined with the GOES-11 image, taken July 6 at 0400 Zulu Time (12:00 a.m. EDT). The TRMM data shows the horizontal pattern of rain intensity within Blanca. The heaviest rainfall is depicted in red and purple, between 1.4 and 1.6 inches per hour, and is around the center of the storm. The infrared GOES-11 image shows Blanca's clouds. Infrared imagery was used because the data was captured at night, and the clouds would not have been visible. Infrared light enables the satellite to "read" the temperature of the clouds to get an image of them.

At 11 a.m. EDT on Monday, July 6, 2009 the center of Tropical Storm Blanca was about 410 miles south-southwest of the southern tip of Baja California, or near latitude 17.3 north and longitude 112.1 west. Blanca's maximum sustained winds are now near 45 mph with higher gusts. Blanca is moving toward the west-northwest near 10 mph and should continue in that general direction over the next couple of days. Estimated minimum central pressure is 1000 millibars.

The National Hurricane Center notes that "atmospheric conditions appear favorable for some additional strengthening over the next 24-36 hours. However, Blanca should reach sub-26 Celsius ocean waters (78 degrees Fahrenheit) in a day or so...which should cause gradual weakening." Tropical cyclones need warm ocean surface temperatures near 80 F to maintain strength.